Bottom Line:
The MRFs and MEF2 families are also critical for the phenotypic differences between the two pig breeds.Overall, this study contributes to elucidating the mechanism underlying muscle development, which could provide valuable information for pig meat quality improvement.The raw data have been submitted to Gene Expression Omnibus (GEO) under series GSE25406.

ABSTRACTUnderstanding the dynamics of muscle transcriptome during development and between breeds differing in muscle growth is necessary to uncover the complex mechanism underlying muscle development. Herein, we present the first transcriptome-wide longissimus dorsi muscle development research concerning Lantang (LT, obese) and Landrace (LR, lean) pig breeds during 10 time-points from 35 days-post-coitus (dpc) to 180 days-post-natum (dpn) using Solexa/Illumina's Genome Analyzer. The data demonstrated that myogenesis was almost completed before 77 dpc, but the muscle phenotypes were still changed from 77 dpc to 28 dpn. Comparative analysis of the two breeds suggested that myogenesis started earlier but progressed more slowly in LT than in LR, the stages ranging from 49 dpc to 77 dpc are critical for formation of different muscle phenotypes. 595 differentially expressed myogenesis genes were identified, and their roles in myogenesis were discussed. Furthermore, GSK3B, IKBKB, ACVR1, ITGA and STMN1 might contribute to later myogenesis and more muscle fibers in LR than LT. Some myogenesis inhibitors (ID1, ID2, CABIN1, MSTN, SMAD4, CTNNA1, NOTCH2, GPC3 and HMOX1) were higher expressed in LT than in LR, which might contribute to more slow muscle differentiation in LT than in LR. We also identified several genes which might contribute to intramuscular adipose differentiation. Most important, we further proposed a novel model in which MyoD and MEF2A controls the balance between intramuscular adipogenesis and myogenesis by regulating CEBP family; Myf5 and MEF2C are essential during the whole myogenesis process while MEF2D affects muscle growth and maturation. The MRFs and MEF2 families are also critical for the phenotypic differences between the two pig breeds. Overall, this study contributes to elucidating the mechanism underlying muscle development, which could provide valuable information for pig meat quality improvement. The raw data have been submitted to Gene Expression Omnibus (GEO) under series GSE25406.

Mentions:
Morphological differences among muscle samples were studied by histological section (Figure 1). At 35 dpc, few primary fibers were present in LT but not in LR. The cross-section of presumptive primary fibers observed at 35 dpc enlarged at 49 dpc, and the fiber bundles were isolated by connective tissue in both breeds. The secondary fibers formed around primary fibers at 63 dpc and gradually increased until 91 dpc; more fibers were found in LR. At 91 dpc, it was difficult to distinguish primary fibers from secondary fibers and presumptive muscle bundles began to emerge. Moreover, muscle fiber diameter of LR is larger than LT during this period (Figure 1, LT5 and LR5). During postnatal development, the muscle phenotypes still changed from 91 dpc to 28 dpn. The muscle fibers grew more rapidly and larger cross-section areas were found in LR than in LT (Figure 1, LT6–LT10 and LR6–LR10).

Mentions:
Morphological differences among muscle samples were studied by histological section (Figure 1). At 35 dpc, few primary fibers were present in LT but not in LR. The cross-section of presumptive primary fibers observed at 35 dpc enlarged at 49 dpc, and the fiber bundles were isolated by connective tissue in both breeds. The secondary fibers formed around primary fibers at 63 dpc and gradually increased until 91 dpc; more fibers were found in LR. At 91 dpc, it was difficult to distinguish primary fibers from secondary fibers and presumptive muscle bundles began to emerge. Moreover, muscle fiber diameter of LR is larger than LT during this period (Figure 1, LT5 and LR5). During postnatal development, the muscle phenotypes still changed from 91 dpc to 28 dpn. The muscle fibers grew more rapidly and larger cross-section areas were found in LR than in LT (Figure 1, LT6–LT10 and LR6–LR10).

Bottom Line:
The MRFs and MEF2 families are also critical for the phenotypic differences between the two pig breeds.Overall, this study contributes to elucidating the mechanism underlying muscle development, which could provide valuable information for pig meat quality improvement.The raw data have been submitted to Gene Expression Omnibus (GEO) under series GSE25406.

ABSTRACTUnderstanding the dynamics of muscle transcriptome during development and between breeds differing in muscle growth is necessary to uncover the complex mechanism underlying muscle development. Herein, we present the first transcriptome-wide longissimus dorsi muscle development research concerning Lantang (LT, obese) and Landrace (LR, lean) pig breeds during 10 time-points from 35 days-post-coitus (dpc) to 180 days-post-natum (dpn) using Solexa/Illumina's Genome Analyzer. The data demonstrated that myogenesis was almost completed before 77 dpc, but the muscle phenotypes were still changed from 77 dpc to 28 dpn. Comparative analysis of the two breeds suggested that myogenesis started earlier but progressed more slowly in LT than in LR, the stages ranging from 49 dpc to 77 dpc are critical for formation of different muscle phenotypes. 595 differentially expressed myogenesis genes were identified, and their roles in myogenesis were discussed. Furthermore, GSK3B, IKBKB, ACVR1, ITGA and STMN1 might contribute to later myogenesis and more muscle fibers in LR than LT. Some myogenesis inhibitors (ID1, ID2, CABIN1, MSTN, SMAD4, CTNNA1, NOTCH2, GPC3 and HMOX1) were higher expressed in LT than in LR, which might contribute to more slow muscle differentiation in LT than in LR. We also identified several genes which might contribute to intramuscular adipose differentiation. Most important, we further proposed a novel model in which MyoD and MEF2A controls the balance between intramuscular adipogenesis and myogenesis by regulating CEBP family; Myf5 and MEF2C are essential during the whole myogenesis process while MEF2D affects muscle growth and maturation. The MRFs and MEF2 families are also critical for the phenotypic differences between the two pig breeds. Overall, this study contributes to elucidating the mechanism underlying muscle development, which could provide valuable information for pig meat quality improvement. The raw data have been submitted to Gene Expression Omnibus (GEO) under series GSE25406.